Orthodontic appliance by using a shape memory polymer

ABSTRACT

Disclosed is an orthodontic appliance for straightening misaligned teeth. The orthodontic appliance is made of a shape memory polymer, and is formed in a cap-shaped tray capable of covering the maxillary or mandibular teeth. An original shape of the tray-type orthodontic appliance made of the shape memory polymer is identical to that of perfectly aligned teeth obtained after orthodontic treatment, and a temporarily formed shape of the tray-type orthodontic appliance is identical to that of the teeth alignment of a patient before orthodontic treatment. The tray-type orthodontic appliance is restored to the original shape memorized at a temperature above a specified glass transition temperature. The orthodontic appliance can be easily manufactured to perform orthodontic treatment, also providing appealing esthetics, in which the orthodontic appliance can be colored to be identical to a tooth with inexpensive manufacturing cost.

TECHNICAL FIELD

The present invention relates to an orthodontic appliance, and inparticular, to an orthodontic appliance made of a shape memory polymercapable of being restored to its original shape at a temperature lowerthan a predetermined temperature.

BACKGROUND ART

In general, malocclusion refers to the state in which teeth are crookedor poorly aligned. Orthodontics refers to the treatment forstraightening teeth. In case of the malocclusion of teeth or teethmisalignment, the following problems exist: unappealing appearance;difficulty in or when chewing food; and poor pronunciation of words. Inorder to eliminate these problems, various orthodontic appliances havebeen developed.

Several types of orthodontic appliances, which include removable, fixed,and extra-oral orthodontic appliances are generally used and well knownin the art.

First of all, a removable orthodontic appliance is one that a wearer canapply or put into his or her mouth by himself or herself, and generallyhas a large size. The wearer also has to pay close attention to itsmaintenance.

A fixed orthodontic appliance is one that it is attached and fixed tothe teeth. The size of the fixed orthodontic appliance is smaller thanthat of the removable orthodontic appliance and can correctly implementorthodontic treatment. Generally, the fixed orthodontic applianceincludes a bracket serving as a metal support, and a wire. The bracketis attached to the surface of the teeth and the wire is inserted intothe slots of the bracket so that pushing or pulling the wire makes aposition of teeth slowly altered, thereby correcting the misalignedteeth. Although the most typical fixed orthodontic appliance employs ametal bracket, there are other types employing a gold bracket or aceramic bracket.

An extra-oral orthodontic appliance is used in conjunction with aremovable or fixed orthodontic appliance, in order to obtain asupporting or movement force from external anatomical structures uponthe movement of the teeth.

Meanwhile, since the above-mentioned orthodontic appliances are mainlymade of metal, a drawback exists in that the wearer must wear unsightlybrackets and wires for a significant period of time.

In order to remedy this drawback, a lingual orthodontic technique hasbeen developed where a bracket is attached to the internal side of theteeth facing the tongue, which prevents the orthodontic appliance frombeing seen from the exterior. (See Japanese Utility-Model PublicationNo. Sho 57-44967, U.S. Pat. No. 4,337,037, and Korean Patent ApplicationNo. 1999-7009678.)

However, this lingual orthodontic technique has the following problems:the bracket must be separately manufactured to conform to the grooveformed on the inside of the teeth; precision in treatment is required,since the wire is threaded in a narrow oral cavity; and since thebracket and wire are attached within the oral cavity, it is difficult tochew food and the wearer has a speech impediment for an extended periodof time after performing the treatment.

Furthermore, since a fixed orthodontic appliance requires the periodicadjustment (i.e., pushing or pulling) on the wire mounted to thebracket, continuous maintenance is required. In every instance where theorthodontic appliance is maintained, the wearer will suffer pain.

DISCLOSURE OF THE INVENTION

Therefore, an object of the present invention is to solve the problemsinvolved in the prior art, and to provide an orthodontic appliance usinga shape memory polymer.

Another object of the present invention is to provide an orthodonticappliance capable of being easily mounted to the patient's (or wearer's)teeth, so that the patient (or wearer) does not suffer from pain to hisor her mouth.

Still another object of the present invention is to provide anorthodontic appliance having no additional adjusting process, such aspushing or pulling, after it is mounted to the patient's (or wearer's)teeth.

Still another object of the present invention is to provide aninexpensive orthodontic appliance made of material having the same coloras that of teeth or a transparent color, thereby making it lessnoticeable.

In order to accomplish the above-mentioned objects, the presentinvention provides an orthodontic appliance for straightening misalignedteeth made of a shape memory polymer and formed in a cap-shaped traycapable of covering maxillary or mandibular teeth, wherein the originalshape of the tray-type orthodontic appliance made of the shape memorypolymer is identical to that of perfectly aligned teeth obtained afterorthodontic treatment, and a temporarily formed shape of the tray-typeorthodontic appliance is identical to that of the alignment of apatient's teeth before orthodontic treatment, and wherein the tray-typeorthodontic appliance is restored to the original shape at a temperatureabove a specified glass transition temperature.

The orthodontic appliance is adapted to cover teeth or both of teeth andpalate when the appliance is used for a maxilla.

In another aspect of the present invention, a molar upstandingorthodontic appliance made of a shape memory polymer and formed in acap-shaped tray capable of covering only predetermined teeth isprovided, wherein the original shape of the tray-type orthodonticappliance made of the shape memory polymer is identical to that ofperfectly aligned teeth obtained after orthodontic treatment, and atemporarily formed shape of the tray-type orthodontic appliance isidentical to that of the alignment of the patient's teeth beforeorthodontic treatment, and wherein the tray-type orthodontic applianceis restored to its original shape at a temperature above a specifiedglass transition temperature.

In still another aspect of the present invention, there is provided anorthodontic appliance for straightening misaligned teeth formed in aband having a predetermined width and length, wherein the band-typeorthodontic appliance made of a shape memory polymer is restored to itsoriginal shape at a temperature above a specified glass transitiontemperature.

In still another aspect of the present invention, there is provided anorthodontic appliance for straightening misaligned teeth made of a shapememory polymer having a predetermined glass transition temperature andformed in a mouthguard capable of completely covering maxillary ormandibular teeth, wherein the original shape of the mouthguard-typeorthodontic appliance made of a shape memory polymer is identical tothat of perfectly aligned teeth obtained after orthodontic treatment,and a temporarily formed shape of the mouthguard-type orthodonticappliance is identical to that of the alignment of the patient's teethbefore orthodontic treatment, wherein the mouthguard-type orthodonticappliance is restored to its original shape at a temperature above aspecified glass transition temperature.

In still another aspect of the present invention, there is provided amethod for manufacturing a tray-type orthodontic appliance made of ashape memory polymer having a first and second glass transitiontemperature the method comprising the steps of: forming the tray-typeorthodontic appliance to provide the orthodontic appliance with a shapeidentical to that of perfectly aligned teeth at a temperature above thefirst glass transition temperature; cooling the orthodontic appliance tofix the shape thereof; forming the orthodontic appliance to have a shapeidentical to that of the patient's teeth as presently aligned at atemperature above the second glass transition temperature; and coolingthe orthodontic appliance to fix the shape thereof.

According to the present invention, the orthodontic appliance may beeasily mounted to the patient's teeth with appealing esthetics. Inaddition, the patient suffers no pain, since the malocclusion of teethor teeth misalignment is straightened by use of a restoring force of theshape memory polymer.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the present invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, other features and advantages of the presentinvention will become more apparent by describing the preferredembodiment thereof with reference to the accompanying drawings, inwhich:

FIG. 1 is a perspective view illustrating a bracket and a wire of anorthodontic appliance according to a first preferred embodiment of thepresent invention;

FIG. 2 is a view illustrating the state in which the orthodonticappliance shown in FIG. 1 is applied to teeth;

FIG. 3 is a perspective view illustrating a band-type orthodonticappliance according to a second preferred embodiment of the presentinvention;

FIG. 4 is a view illustrating the state in which the orthodonticappliance shown in FIG. 3 is applied to teeth;

FIG. 5 is a perspective view illustrating a tray-type orthodonticappliance according to a third preferred embodiment of the presentinvention;

FIG. 6A is a front view showing a conventional orthodontic method foruprighting a molar;

FIG. 6B is a front view showing the state of molar uprighting using atray-type orthodontic appliance according to the present invention;

FIG. 7 is a perspective view illustrating a tray-type orthodonticappliance according to a fourth preferred embodiment of the presentinvention;

FIGS. 8A and 8B are respectively perspective views of aquadrant-tray-type orthodontic appliance and an anterior orthodonticappliance according to the present invention; and

FIGS. 9A and 9B are perspective and cross sectional views of amouthguard-type orthodontic appliance according to a fifth preferredembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention; examples of which are illustrated in the accompanyingdrawings. In the embodiments, similar parts are shown by theircorresponding reference numerals throughout the drawings, in whichadditional explanation thereof will be omitted.

A shape memory polymer used as material for an orthodontic appliance ofthe present invention will now be described in detail.

Shape memory is the ability of a material to remember its original shapeby imparting a particular form to the polymer in a solid state, thencooling the article to a glass transition temperature of the polymer ora lower temperature to set the shape of the new form, and heating thearticle to a temperature above the glass transition temperature of thepolymer to recover its original shape. The materials known to have theseproperties are shape memory alloys, such as Nitinol, or a shape memorypolymer.

International Patent Application No. PCT/US 99/03923 discloses shapememory polymer compositions, and methods of preparation and use thereof.U.S. Pat. No. 5,506,300 issued to Ward et al., entitled “Compositionsthat soften at predetermined temperatures and the method of making thesame,” discloses a shape memory polymer having a predetermined glasstransition temperature.

Research on shape memory polymers have attracted a considerable amountof attention, due to its many advantageous characteristics: low densityof 1.0 to 1.3 g/cm³; high ratio of shape recovery; easy manipulation;transparency; dyeing ability; and inexpensiveness.

Mechanism of the above shape memory polymer is absolutely different fromthat of the shape memory alloy. In general, the shape memory property ofthe polymer is caused when the polymer, such as rubber or plastics,memorizes the absorbed stress and strain by use of viscoelasticitydepending upon time in relation to stress and strain. Considering themechanism of the shape memory polymer, if the shape memory polymer isapplied with a certain level of pressure, it can expand five or sixtimes its original size, just like rubber. If the applied pressure isrelieved, the polymer returns to its original size. The elasticity asdescribed above is lost at very low temperatures, such as −196° C.Accordingly, if the expanded shape memory polymer is cooled at such alow temperature, that particular shape is fixed. Below the glasstransition temperature T_(g), the polymer does not return to itsoriginal shape. Meanwhile, the original shape is recovered by heatingthe polymer above the glass transition temperature.

The recovery of the original shape is based on thermal, photo orchemical response depending upon the type of polymer, which arerespectively named the thermal-responsive shape memory effect, thephoto-responsive shape memory effect, and the chemo-responsive shapememory effect.

The differences between a common polymer and the shape memory polymerwill now be discussed.

The formation characteristic of a common polymer is in a solid glassstate at a temperature lower than the glass transition temperature,while existing in a rubber state having a low modulus of elasticity,thereby making it easy to form at a high temperature. In addition, afterthe common polymer is deformed at a high temperature, if the appliedload is relieved and then the polymer is cooled and once again heated,it will be difficult for the deformed material to recover its originalshape, since the formed material exists in the same shape as the cooledshape.

The shape memory polymer has a two-phase structure capable of beingreversibly repeated between the softening and the hardening phases. As aresult, in accordance with the temperature variation and a setting point(freezing point), which will interfere with the flow of the polymer, itis possible to recover the residual formation when the temperature israised. It is an object of the present invention to provide anorthodontic appliance manufactured by use of a shape memory effect of athermal-responsive shape memory polymer, among the several differentshape memory polymers mentioned above.

Reference will now be made in detail to the orthodontic appliancemanufactured of the shape memory polymer according to the preferredembodiments of the present invention.

FIRST EMBODIMENT

The orthodontic appliance according to the first preferred embodiment ofthe present invention will now be described.

FIG. 1 is a perspective view illustrating the shape of teeth with abracket attached. FIG. 2 is a view illustrating the state in which theorthodontic appliance shown in FIG. 1 is applied to the teeth.

As shown in FIGS. 1 and 2, the orthodontic appliance of the shape memorypolymer according to the present invention is a wire mounted to a slotof the bracket attached to the surface of the teeth, and the wire of thepresent invention is characterized by being made of a shape memorypolymer having a glass transition temperature of 35° C. At that time,the glass transition temperature of the shape memory polymer used formanufacturing the wire for the bracket is set to 35° C., which is thetemperature of the oral cavity of a wearer. When the wire for thebracket is installed in the oral cavity, an elastic force is produced atthe wire, so that it may recover to its ideal shape memorized previouslyin order to gradually correct the misaligned teeth of the wearer.

A method of manufacturing the wire by use of the shape memory polymerwill now be described.

Powders or pellets of the shape memory polymer are melted, and are thenformed to have its original shape. If necessary, the crosslinking of theshape memory polymer may be achieved using a crosslinking agent or aphoto-crosslinker. In other words, the shape memory polymer is shaped tothe wire according to the present invention.

The wire having its original shape is then applied with stress andstrain at a temperature above the glass transition temperature, therebyforming it to a desired shape. When the formed wire is properly bended,a bended length is predetermined in a range for providing the properelastic force to the teeth.

The shape temporarily formed by the stress and strain is then cooled ata temperature lower than the glass transition temperature.

A wire manufactured using the shape memory polymer has the followingbenefits: the wire may be formed to be transparent; the wire may be dyedwith the same color as teeth; manufacturing cost can be reduced; and thewire can be easily manufactured. In addition, since the shape memory hasa constant elastic force, a mild force is continuously applied to theteeth, thereby correcting the misaligned teeth.

The wire manufactured by the above-mentioned method is installed to theslot of the bracket, which is attached to the surface of the teeth inthe oral cavity, in a temporarily formed shape. If the wire installed tothe slot of the bracket is heated at a temperature higher than the glasstransition temperature by the temperature of the oral cavity, a constantelastic force is applied to the teeth when the shape memory effectrecovers to its original shape. Proper pressure is continuously appliedto the teeth by the elastic force, thereby correcting the misalignedteeth. Contrary to a conventional orthodontic appliance, the presentinvention may easily carry out orthodontic treatment, without need ofperiodic adjustment, such as pushing or pulling, on a wire mounted to abracket. Furthermore, the present invention may carry out orthodontictreatment without causing pain to the wearer.

Since the wire made of the shape memory polymer, according to theembodiment of the present invention, may be utilized together with thebracket made of ceramic, the present invention may manufacture the fixedorthodontic appliance, so that it is not visually distinctive.

SECOND EMBODIMENT

The second preferred embodiment of the present invention relates to aband-type orthodontic appliance. The band-type orthodontic appliancewill now be described with reference to FIGS. 3 and 4.

FIG. 3 is a perspective view illustrating the band-type orthodonticappliance according to the present invention.

The band-type orthodontic appliance 300 has a desired width and length,and is made of the shape memory polymer. Preferably, the glasstransition temperature of the shape memory polymer forming theorthodontic appliance 300 is 35° C.

The original shape of the band-type orthodontic appliance is identicalto that of perfectly aligned teeth obtained after orthodontic treatment,and a temporarily formed shape of the band-type orthodontic appliance isidentical to that of the patient's teeth as aligned before orthodontictreatment. If the orthodontic appliance is heated at a temperaturehigher than the glass transition temperature, the band-type orthodonticappliance according to the embodiment is restored to its original shape,which is identical to teeth that are perfectly aligned after orthodontictreatment.

FIG. 4 is a view illustrating the state in which the orthodonticappliance shown in FIG. 3 is applied to the teeth. As shown in FIG. 4,the band-type orthodontic appliance is attached to the surface of theteeth to be corrected. Preferably, a dental adhesive, i.e., a composite,is used so as to attach the orthodontic appliance to the surface of theteeth.

The method of manufacturing the band-type orthodontic appliance,according to the embodiment, is identical to that of the firstembodiment. Thus, the description thereof is omitted herein.

Since the band-type orthodontic appliance of the embodiment is attachedto the surface of the teeth by use of the adhesive without attaching thebracket, orthodontic treatment may be easily performed, and expenses maybe reduced. In addition, if the band-type orthodontic appliance is dyedwith the same color as teeth, the orthodontic appliance will be lessnoticeable. Furthermore, the teeth are applied with a constant elasticforce when the shape memory effect recovers to its original shape.Proper pressure is continuously applied to the teeth by such an elasticforce, thereby correcting the misaligned teeth. Therefore, the presentinvention may easily carry out orthodontic treatment, without need ofperiodically tightening the orthodontic appliance, which is required ina conventional application. Furthermore, the present invention may carryout orthodontic treatment without causing pain to the wearer.

The band-type orthodontic appliance of the present invention may beapplied to the orthodontic treatment of diastema, crowding of teeth,molar uprighting or the like.

THIRD EMBODIMENT

The third preferred embodiment of the present invention relates to atray-type orthodontic appliance made of a shape memory polymer, whichwill be referred to as a nasopalatinal tray-type orthodontic appliancein order to distinguish it from the fourth embodiment. The tray-typeorthodontic appliance according to the present invention will now bedescribed with reference to FIG. 5.

FIG. 5 is a perspective view illustrating the state in which thenasopalatinal tray-type orthodontic appliance 500, according to theembodiment, is disposed on the upper portion of the teeth.

As shown in FIG. 5, the nasopalatinal tray-type orthodontic appliance,according to the embodiment, is made of the shape memory polymer, andhas a shape capable of covering the entire surface of the teeth.

Preferably, the shape memory polymer, according to the presentinvention, has a glass transition temperature of 35° C. Also, theoriginal shape of the tray-type orthodontic appliance is identical toteeth that are perfectly aligned after orthodontic treatment, and atemporarily formed shape of the tray-type orthodontic appliance isidentical to that of the patient's teeth as aligned before orthodontictreatment.

The operation of the nasopalatinal tray-type orthodontic applianceaccording to the present invention will now be described.

Since the temporarily formed shape of the tray-type orthodonticappliance is identical to that of the patient's teeth as aligned beforeorthodontic treatment at room temperature or below 35° C., theorthodontic appliance with the temporarily formed shape is placed on thepatient's teeth. The orthodontic appliance is installed in the oralcavity. The temperature of the orthodontic appliance is increased to atemperature higher than that of the oral cavity, for example 35° C., andthen the orthodontic appliance recovers to its memorized ideal originalshape. In the course of transforming the temporarily formed shape to theideal original shape, the orthodontic appliance gradually applies anelastic force to the teeth, thereby correcting the misaligned teeth.

FOURTH EMBODIMENT

A palatal tray-type orthodontic appliance according to the presentinvention will now be described with reference to FIG. 7.

The palatal tray-type orthodontic appliance, according to theembodiment, is to cover the entire palate, as well as to cover theteeth, which is contrary to the orthodontic appliance of the thirdembodiment. The palatal tray-type orthodontic appliance of thisembodiment has a shape different from the nasopalatinal tray-typeorthodontic appliance described above. However, the material andmanufacturing method thereof are identical to those of the nasopalatinaltray-type orthodontic appliance. Therefore, the description thereof willbe omitted.

Now, the application field of the nasopalatinal and palatal tray-typeorthodontic appliances described above will be described in detail.

1) Crowding of Teeth

The embodiments may be used to solve the crowding of the teeth occurringat a mixed dentition or a permanent dentition. In the case where severecrowding exists, the palatal tray-type orthodontic appliance, which morestrongly reacts against the force generated from the movement of teethduring correction, is preferably used. Meanwhile, in the case of theminor teeth crowding, the nasopalatinal tray-type orthodontic applianceis preferably used.

In particular, if the present embodiments are carried out together withproximal disking, a better result will be obtained. The reason is that alower force will be applied relative to non-disked cases in moving theteeth.

2) Arch Expansion

The present embodiments may be used for the treatment of arch expansiondue to the opening of a mid-palatal suture in the mixed dentition.Meanwhile, since greater force is needed upon opening the mid-palatalsuture at the permanent dentition, the palatal tray-type orthodonticappliance may be used for the treatment when there is a slight amount ofarch expansion.

In the case where the arch expansion is not caused by a skeletalproblem, but rather an inherited problem of the teeth, it is preferableto treat narrow arch by use of a nasopalatinal tray-type orthodonticappliance.

3) Retainer

The orthodontic appliance of the present invention may be used as aretainer or a device for minor movement of the teeth after commonorthodontic treatment. For example, if the retainer is shaped like thetray-type orthodontic appliance according to the present invention, theoral hygiene of the patient will be improved, and appearance will beimproved because of its transparency.

4) Space Maintainer

Mesial inclination of a permanent first molar resulting from an earlymissing primary molar or extraction of a primary molar will be preventedby using the orthodontic appliance of the embodiment.

This case does not concern a tray covering the entire arch. A quadranttray covering a certain portion of the arch may be satisfactory in thiscase, as shown in FIG. 8A. Preferably, the quadrant tray is adapted tocover half of the maxillary arch or mandibular arch.

5) Molar Uprighting

After the first permanent first molar is extracted, which has not beentreated for a long time, the posteriorly positioned tooth adjacent tothe missing tooth will topple down forwardly. Thus, the anteriorlypositioned tooth is moved rearward. The molar uprighting may be used tosolve this problem using the orthodontic appliance according to theembodiments.

FIG. 6A is a front view showing a conventional orthodontic method foruprighting the molar. FIG. 6B is a front view showing the state of molaruprighting using the tray-type orthodontic appliance according to thepresent invention.

As shown in FIG. 6A, the conventional orthodontic method utilizes aspring or wire to carry out the molar uprighting. However, the presentinvention utilizes the tray-type orthodontic appliance manufactured bythe shape memory polymer, thereby easily carrying out the molaruprighting.

As shown in FIG. 6A, a partial tray-type orthodontic appliance ispreferably utilized to carry out the molar uprighting, instead of atray-type orthodontic appliance. The partial tray is adapted to encloseonly the anteriorly and posteriorly positioned teeth (i.e., the desiredteeth) adjacent to the missing tooth.

6) Diastema Closing

Diastema may be closed by use of the orthodontic appliance according tothe embodiments. As shown in FIG. 8B, diastema may be treated by usingthe anterior orthodontic appliance.

The anterior orthodontic appliance is adapted to enclose six teeth fromthe left canine to the right canine.

FIFTH EMBODIMENT

A mouthguard-type orthodontic appliance according to the presentinvention will now be described with reference to FIGS. 9A and 9B.

FIG. 9A is a perspective view of the mouthguard-type orthodonticappliance according to a fifth preferred embodiment of the presentinvention. FIG. 9B is a cross-sectional view taken along a line A-B inFIG. 9A, in which the maxillary and mandibular teeth are shown with theorthodontic appliance mounted thereon.

As shown in FIG. 9A, the mouthguard-type orthodontic appliance of theembodiment is made in the shape of a mouthguard in which the tray isintegrally formed with the maxillary and mandibular teeth, and is madeof the shape memory polymer. The characteristics of the shape memorypolymer are substantially identical to those provided by otherembodiments, the description of which will be omitted. In addition, themanufacturing method thereof is substantially identical to thatmentioned in other embodiments, the description of which will also beomitted.

The mouthguard-type orthodontic appliance using the shape memorypolymer, according to the embodiment, may move the relationship of themaxillary and mandibular teeth, in cases of teeth-borne problems,skeletal mandibular protrusion and skeletal maxillary protrusion.

The mouthguard-type orthodontic appliance may be used in cases ofmaxillary and mandibular cross-bite, maxillary and mandibular archexpansion, or maxillary and mandibular arch construction. In addition,the mouthguard-type orthodontic appliance may intrude the erupted toothin which the treatment thereof is impossible by a conventionalpositioner, i.e., an erupted tooth resulting from an early missing toothor extraction of a tooth on opposite arches.

Meanwhile, the shape memory polymer used for manufacturing theorthodontic appliance, according to the present invention, may becomposed of at least two polymers of which the glass transitiontemperature is different from each other, specifically a fundamentalpolymer and an additive polymer. Accordingly, the shape memory polymercomposed of a polymer composition has two glass transition temperatures.

Preferably, a block copolymer having a hard segment and a soft segmentis used as the fundamental polymer. For example, polyurethane, such aspolyester urethane, polyether urethane and so forth may be used.Preferably, the glass transition temperature of the fundamental polymeris 25° C., which is lower than the body temperature.

Also, a thermosetting polymer may be used as the additive polymer. Forexample, DGEBA-type epoxy resin, polystyrene/acrylonitrile copolymer,and so forth may be used. Preferably, the glass transition temperatureof the additive polymer is above 35° C.

Physical properties (i.e., the glass transition temperature) of theshape memory polymer may be regulated by adjusting the mixing ratio ofthe polymers comprising the polymer blend.

The method of manufacturing the orthodontic appliance using the shapememory polymer having two glass transition temperatures, as describedabove, will now be described.

The two glass transition temperatures are set to first and second glasstemperatures, respectively. The first glass transition temperature isset to 35° C., which is the glass transition temperature of the additivepolymer, while the second glass transition temperature is set to 25° C.,which is the glass transition temperature of the fundamental polymer.

First of all, the tray-type orthodontic appliance is formed to have ashape identical to that of perfectly aligned teeth at a temperatureabove the first glass transition temperature. The orthodontic applianceis then cooled to fix the shape thereof. The orthodontic appliance isformed to have a shape identical to that of the presently aligned teethof a patient at a temperature above the second glass transitiontemperature. The orthodontic appliance is then cooled to fix the shapethereof.

The orthodontic appliance manufactured by the above-mentioned method ismaintained in the shape identical to that of the presently aligned teethof the patient at a temperature below the second glass transitiontemperature. The orthodontic appliance is maintained in the shapeidentical to perfectly aligned teeth at a temperature above the firstglass transition temperature. Accordingly, while the orthodonticappliance of the present invention is maintained in the shape identicalto the presently aligned teeth of the patient at room temperature or lowtemperature, if it is positioned in the oral cavity of the patient, theorthodontic appliance is formed to have the memorized ideal shape. Atthat time, an elastic force is produced from the process, therebycorrecting the misaligned teeth.

Meanwhile, the orthodontic appliance of the present invention may beremoved from the mouth of the patient, if necessary, and then formed tohave a shape identical to the present teeth alignment below the glasstransition temperature. At that time, in order to form the appliance toits original shape, it may be compressed by use of an air compressor,compressing tools, or by hand. If the orthodontic appliance is againplaced in the oral cavity, it will again recover to the form for idealteeth alignment.

Although the material regarding the block copolymer and thermosettingpolymer is suggested herein, these are merely illustrated to help in theunderstanding and the description of the present invention, and do notrestrict the scope of the present invention.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers allmodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

Industrial Applicability

The orthodontic appliance made of the shape memory polymer according tothe present invention can be easily manufactured to perform orthodontictreatment, and can be manufactured at an inexpensive cost. In addition,the orthodontic appliance of the shape memory polymer also providesappealing esthetics, which can be colored to be identical to a tooth, sothat it is not apparently distinguishable from natural teeth.

Since the orthodontic appliance memorizes the shape of perfectly alignedteeth at the temperature of the oral cavity, a constant elastic force isapplied to the teeth when the shape memory effect recovers to itsoriginal shape. Proper pressure is continuously applied to the teeth bythe elastic force, thereby correcting the misaligned teeth. Therefore,the present invention may easily carry out orthodontic treatment,without need of periodic tightening as in a conventional orthodonticappliance. Furthermore, the present invention may carry out orthodontictreatment, without causing pain to the wearer.

1. An orthodontic appliance for straightening misaligned teeth made of a shape memory polymer and formed in a cap-shaped tray capable of covering maxillary or mandibular teeth, wherein an original shape of the tray orthodontic appliance made of the shape memory polymer is identical to that of perfectly aligned teeth obtained after orthodontic treatment, and a temporarily formed shape of the tray orthodontic appliance is identical to that of a patient's teeth before orthodontic treatment, and wherein the tray-type orthodontic appliance is restored to the original shape memorized at a temperature above a specified glass transition temperature.
 2. The orthodontic appliance of claim 1, wherein the orthodontic appliance is formed in the cap-shaped tray capable of completely covering the entire maxillary or mandibular teeth.
 3. The orthodontic appliance of claim 1, wherein the orthodontic appliance is formed in the cap-shaped tray capable of selectively covering predetermined teeth among the maxillary or mandibular teeth.
 4. The orthodontic appliance of claim 3, wherein the orthodontic appliance is formed in the cap-shaped tray capable of covering anterior teeth among the maxillary or mandibular teeth.
 5. The orthodontic appliance of claim 1, wherein the orthodontic appliance is adapted to cover teeth and a palate when the appliance is used for a maxilla.
 6. An orthodontic appliance for straightening misaligned teeth formed in a band having a predetermined width and length, wherein the band orthodontic appliance made of a shape memory polymer is restored to an original shape memorized at a temperature above a specified glass transition temperature.
 7. An orthodontic appliance for straightening misaligned teeth made of a shape memory polymer having a predetermined glass transition temperature and formed in a mouthpiece capable of completely covering maxillary or mandibular teeth, wherein an original shape of the mouthpiece orthodontic appliance made of the shape memory polymer is identical to that of perfectly aligned teeth obtained after orthodontic treatment, and a temporarily formed shape of the mouthpiece orthodontic appliance is identical to that of a patient's teeth before orthodontic treatment, and wherein the mouthpiece orthodontic appliance is restored to the original shape memorized at a temperature above a specified glass transition temperature.
 8. The orthodontic appliance of any one of claims 1 to 7, wherein the shape memory polymer comprises a polymer composition consisting of a base polymer and a second polymer.
 9. The orthodontic appliance of claim 8, wherein the base polymer comprises a block copolymer.
 10. The orthodontic appliance of claim 8, wherein the glass transition temperature of the base polymer is below 25° C.
 11. The orthodontic appliance of claim 8, wherein the second polymer comprises a thermosetting polymer.
 12. The orthodontic appliance of claim 8, wherein the glass transition temperature of the second polymer is above 35° C.
 13. The orthodontic appliance of any one of claims 1 to 7, wherein a color of the orthodontic appliance is identical to that of the teeth or is transparent.
 14. The orthodontic appliance of any one of claims 1 to 7, wherein the glass transition temperature of the shape memory polymer is 35° C.
 15. A method for manufacturing a tray orthodontic appliance made of a shape memory polymer having a first-and second glass transition temperature, the method comprising the steps of: forming the tray-type orthodontic appliance to provide the orthodontic appliance with a shape identical to that of perfectly aligned teeth at a temperature above the first glass transition temperature; cooling the orthodontic appliance to fix the shape thereof; deforming the orthodontic appliance to have a shape identical to that of a patient's presently aligned teeth at a temperature above the second glass transition temperature; and cooling the orthodontic appliance to fix the shape thereof.
 16. An orthodontic appliance for straightening misaligned teeth, the orthodontic appliance comprising a bracket attached to the surface of the teeth and a wire mounted to the bracket, wherein the wire is made of a shape memory polymer having a glass transition temperature so that the wire is restored to the original shape memorized at a temperature above the glass transition temperature.
 17. The orthodontic appliance claimed in claim 16, wherein the glass transition temperature is about 35° C.
 18. The orthodontic appliance as claimed in claim 16, wherein the shape memory polymer is a thermal-responsive shape memory polymer or a photo-responsive shape memory polymer. 